Application of radiofrequency (RF) energy has emerged as an important approach to eliminating or reducing the size of undesirable tissue in a subject. When properly directed and localized, RF energy causes controlled hyperthermia that damages or destroys the undesirable tissue without injuring surrounding tissue. For example, RF energy has been used to treat tumors such as metastatic cancer lesions in the liver, to improve obstructive breathing disorders by increasing airway size, and to eliminate undesirable electrical conduction pathways in the heart. See Hyman, Dis. Colon Rectum 43: 279 (2000); Powell et al., Chest 113: 1163-1174; Man et al., Journal of the American College of Cardiology 35: 451-457 (2000); U.S. Pat. Nos. 5,728,094; and 5,849,028, all of which are herein incorporated by reference in their entirety.
RF energy may be used during minimally invasive procedures. For example, RF electrodes may be placed percutaneously (through the skin) to treat a metastatic cancer lesion in the liver. Such a procedure usually requires only local anesthesia with or without conscious sedation. The target lesion may be localized and appropriate RF electrode placement confirmed by standard medical imaging techniques such as ultrasound. Application of measured amounts of RF energy partially or completely destroys the tumor. Using such minimally invasive procedures, it is often possible to treat a subject and discharge him in the same day. In contrast, an open (full surgical) procedure usually requires general anesthesia and many days to weeks of inpatient recovery.
Recently, RF devices have been developed that may be deployed as an RF electrode array. For example, U.S. Pat. No. 6,071,280, herein incorporated by reference, discloses an array of deployable RF electrodes contained within a delivery catheter. The tip of the delivery catheter is inserted in the tissue, for example percutaneously, and properly positioned near the ablation target. The RF electrodes are manually advanced out of the delivery catheter into the target tissue. On deployment, the RF electrodes fan out into an array that defines the volume of tissue to be ablated by RF energy. Similarly, U.S. Pat. No. 5,827,276, herein incorporated by reference, discloses an RF electrode wire array contained within a delivery catheter. Upon catheter insertion, the RF electrode wires are manually advanced out of the catheter and properly positioned within the target tissue.